My 4L XJ16 XJS just failed the emissions test, (Canada). The shop changed 2 upstream oxygen sensors believing this to be the problem, but no improvement, and it failed again. 2 downstream not changed. both cats were changed 1500 miles ago, because it was felt they were the cause of an exhaust odour, (they weren’t). They now suspect the cars computer. Needless to say, it works out quite expensive to keep on replacing components at shop rates untill I get lucky. Can anyone offer an opinion on the likelihood it’s the computer, or suggest what else to look for before I go down that road? It’s a convertible, and an exhaust smell is still present when I stop at intersections etc. possibly unburned gas? No other serious issues with the car, no engine lights, the park idle does go to 1200rpm when the car is hot, but only 800 before it gets up to operating temp. I’m not concerned about the idle speed at this point, but mentioned it in case it may be connected to my emissions problem. I have obtained a pass/fail from the shop, so I am able to buy a sticker and drive the car, but since I will not be able to do that again, I need to resolve the issue. I used a gas additive claimed to help it pass, and ran 400 kilometers minutes prior to test. Any ideas?
Les
Well, on first pass I would guess that the idle speed is connected to the emissions problem. You would expect the idle speed to be higher when cold, then slow down after you meet temperature, so something is amiss.
Does the MY 95 XJS have the x300 OBD control system? I assume it does so that is why you came to this forum to ask. If so, what is the fault code(s) reported? I would sure spend some time diagnosing before I changed the computer. There are a number of sensors involved.
You say no engine lights. If that is the case and you have OBDII, I suspect the “engine light” lamp is burned out. If indeed there are no codes, then what is the failure cause?
Hi, yes, it is OBDll compliant, and the check engine light bulb is fine. According to the shop who did the work, the engine light need not be on in order for it to fail emissions.
It failed on HC. limit is 200, mine was 546
CO% limit is 1 mine was 10.01.
However, a local Jaguar mechanic suggested the coolant sensor as the possible problem, since it is tied in to the injectors. I removed it and cleaned the terminals, and the idle has dropped to 700rpm from 1200. I am optomistic this might be the answer, and I have ordered a new one, so I will have to wait and see. For now, I’m putting this on hold.
Thanks for the help, Les
Great news. It sounds like you may be on to it!.
You know, Les, even with a minimal OBDII reader (the one you can get for less that $50.00 with software) you can read the temperature sensor feedback to compare to the actual coolant temperature as well as a host of other parameters.
If you are going to maintain a car of this age, you should consider arming yourself with a way to diagnose the OBDII.